What was George Ohm's contribution to the field on electricity?

Georg Simon Ohm 1787 - 1854

Georg Simon Ohm discovered how electromotive force works in an electrical circuit, including the relationship that resistance and current play within the circuit.

It was Georg Simon Ohm who defined the fundamental laws of current, resistance and voltage in an electrical circuit by using a basic formula:

I = E/R (This can also be transposed and rewritten): E = I x R (and also) R = E/I

Ohm's Law is one of the most important formulas in electrical theory.